First described during an outbreak in southern Tanzania in 1952, Chikungunya fever is a viral disease spread by mosquitos. Symptoms of the disease include fever and severe joint pain, often accompanied by muscle pain, headache, nausea, fatigue and rash. The name of the disease derives from a verb in the Kimakonde language, meaning “to become contorted”—a reference to the appearance of suffers afflicted with debilitating joint pain. In some instances, the joint pain may persist for several months, or even years. Treatment of the disease focuses on relieving symptoms, as there is no cure. (See WHO Fact sheet No. 327, March 2008)
The virus is transmitted from one human to another by the bites of infected female mosquitos. The most common vectors are Aedes aegypti and Aedes albopictus—two vectors which also transmit other mosquito-borne viruses, including dengue. The Asian tiger mosquito (Aedes albopictus) has also been shown to be an efficient vector for transmission of Chikungunya fever. This latter spec between people. Nonetheless, the insect-based mode of transmission is highly efficient, as evidenced by the infection of nearly 40% of the population of 785,000 individuals during a massive outbreak on La Reunion island in 2005 and 2006. (See WHO Fact sheet No. 327 (March 2008); Science 318:1860-61 (December 2007); and “Information on Aedes albopictus” CDC, Division of Vector-Borne Infectious Diseases)
Chikungunya virus is classified under the Genus Alphavirus, in the Family Togaviridae. Generally speaking, the alphaviruses are enveloped particles containing a genome that consists of a single-stranded, positive-sense RNA molecule of approximately 12 kb. The 5′-end is capped with a 7-methylguanosine while the 3′-end is polyadenylated. Non-structural proteins are translated directly from the 5′ two-thirds of the genomic RNA. A subgenomic positive-strand RNA referred to as 26S RNA, identical to the 3′ one third of the genomic RNA, is transcribed from the negative-stranded RNA intermediate. This latter RNA serves as the mRNA for the synthesis of viral structural proteins. (J. Gen Virol 83:3075-84 (2002))